One-click flaw in Microsoft 365 Copilot could expose emails and corporate data
- Evelyn Carter
- 2 days ago
- 3 min read
A single click by a user on a trusted link pointing to a legitimate Microsoft domain could have allowed an attacker to covertly extract highly sensitive information, including emails, calendar schedules, and indexed files. This security risk stems from a critical vulnerability chain, dubbed SearchLeak, discovered in Microsoft 365 Copilot Enterprise Search.
How does the SearchLeak vulnerability function?
Security researchers at Varonis Threat Labs uncovered this unauthorized exfiltration pathway by chaining three separate software bugs. An attacker can construct a specific URL that forces the AI assistant to search the victim's inbox, retrieve email subject lines, and embed them into an external image URL, requiring absolutely zero typing or second clicks from the user.
Finally, the attack circumvents the website's Content Security Policy (CSP), which typically blocks unknown domains, by exploiting the server-side "Search by Image" feature of Bing (the *.bing.com domain is inherently allowlisted). Bing effectively serves as an exfiltration proxy, fetching the image from the attacker's server with the stolen data encoded right in the URL path, bypassing browser restrictions and logging the data directly for the attacker.
What types of data are at risk of being compromised?
Because Copilot Enterprise operates with the permissions of the logged-in user via Microsoft Graph, an attacker inherits this extensive reach without ever needing to authenticate. The most time-sensitive targets reside directly within the user's inbox, such as one-time passwords (OTP), multi-factor authentication tokens, and password-reset links that remain active for just a few minutes.
Automated scripts parsing the attacker's server logs in real-time can hijack corporate accounts before anyone notices the intrusion. Furthermore, this vulnerability exposes calendar invitations, meeting minutes, and any documents indexed across SharePoint or OneDrive, which often contain sensitive business data such as payroll details, financial earnings, and strategic corporate acquisition plans.
What is the severity and remediation status of this flaw?
Identified globally as CVE-2026-42824, Microsoft has classified this vulnerability as critical. However, its Common Vulnerability Scoring System ratings show some discrepancies, with Microsoft assigning a score of 6.5 while the National Vulnerability Database evaluated it at 7.5. Since Microsoft successfully mitigated the vulnerability directly on its cloud backend, enterprise customers do not need to take manual patching actions or reconfigure their systems.
How can system administrators protect their enterprise environment?
The best recourse is proactive monitoring and mitigation containment. To effectively protect your system from advanced AI-driven threats and manage cloud infrastructure security risks, organizations should establish robust continuous monitoring practices.
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